Meet: Fix releasing media streams, CS fixes

Test Plan:
./phpunit --testsuite=Browser --group=meet
and manually see if the media are released after leving the session, and the same on the room join page

Reviewers: #hkccp_developers, vanmeeuwen

Reviewed By: #hkccp_developers, vanmeeuwen

Subscribers: #hkccp_developers

Differential Revision: https://git.kolab.org/D3520